1. Field of the Invention
The present invention relates to window frames, and more particularly to split mullion window frames adapted for attachment either to building structure about a window opening or to an adjacent frame within such opening.
2. Description of the Prior Art
Formerly, when it was desired to place two or more single- or double-hung windows close together in side-by-side (horizontal or vertical) abutting relationship in a building wall, a transition piece or mullion was used to adjoin adjacent window frames together. With the advent of extruded or molded window frames it has become common to use split mullion frame members which can be joined without the use of a transition piece, thereby reducing the costs of materials and labor for assembly. One example of a split mullion frame design is shown in U.S. Pat. No. 3,769,775 by K. J. Brzezinski.
However, such designs were limited in their application to the joining of multiple windows together. A different configuration of frame member was required for hanging single windows in a building wall or for joining the window frames at the end of an array of windows to a building wall. In the interest of economics it is preferable to have a single configuraion of window frame that is capable of serving both purposes.
At least one manufacturer, Better Bilt Aluminum Products Co. of Smyrna, Tenn., has tried to meet this need by providing a multi-purpose split mullion window jamb design in its Series 500 Vista-Line windows. The salient features of such jambs are shown in cross-section in FIGS. 10 and 11.
In FIG. 11 jambs 110 and 112 of two adjacent window frames are mated together, jamb 110 being the right jamb member of one frame and jamb 112 being the left jamb member of another frame. Jamb 110 has two spaced apart mating flanges 120, 122 extending toward jamb 112. Jamb 112 also has two mating flanges 114, 116 extending toward jamb 110, but flanges 114 and 116 are offset toward each other, so that, when jambs 110 and 112 are mated together, flanges 114, 116 nest between flanges 120, 122.
Referring to FIG. 10, jamb 112 also has a nailing flange 118 positioned between mating flanges 114 and 116. Flange 118 is used for attaching the jamb to a building wall, but is removable by means of a break-off notch 124, so that jambs 110, 112 can be mated together. Once the nailing flange is removed, all that remains is a vestigial stub 126 (FIG. 11). Although it is not shown in the drawings, jamb 110 is also provided with a removable nailing flange like that of jamb 112.
The Series 500 design meets the need for a single configuration split mullion frame, but entails material and tooling costs which it would be preferable to reduce. Use of three separate flanges, together with their supporting structure, requires more material than a lesser number of flanges would require. Also, considerable waste results because the nailing flange must be long enough to extend outwardly of the mating flanges for nailing, and yet be broken off to a length shorter than the mating flanges when mating two jambs together.
It would, therefore, be preferable to reduce the number of flanges required to accomplish the single configuration split mullion frame design. It would also be preferable to reduce the amount of material that is wasted when the nailing flange is removed.
Another disadvantage of previous split mullion window frames is the inadequate thermal barrier they provide at their exposed faces on opposite sides of the building wall. Referring to FIG. 11, mating flanges 114, 120 are positioned at the inner face of the building wall, while flanges 116, 122 are exposed at the outer face of the building wall. Being customarily constructed of extruded aluminum or other thermally conductive material, such frames are poor insulators. Consequently, the exposed outer surfaces of such frames should be shielded from the elements to reduce heat loss.
The Series 500 frame is unsuited to adding such shielding because of the position of the mating flanges. Preferably the nailing and mating flanges of a split mullion window frame would be positioned inwardly of the outer face of the building wall so that the outer surfaces of such flanges can be more easily shielded with insulative material. It would be further preferable if the junction of such frames could be shielded by the siding used on the building wall, such siding extending continuously from the wall over the region of the junctions between window frames.